1. Field of the Invention
The present invention relates to a method for fabricating a bipolar transistor.
2. DESCRIPTION OF THE PRIOR ART
Modern transistors such as bipolar transistors and other devices, whether they are fabricated using polysilicon base technology or conventional technology, use reactive ion etching to open or define regions on the silicon substrate that will be the emitter and base regions.
Transactions of the Metallurgical Society of AIME by Jackson, Jr., Vol. 233, March 1965, pp. 596-602 discloses that in fabricating a buried layer a p-type substrate can have a thermal oxide grown over its surface, and windows can then be etched through the oxide in a photoresist step. The oxide (10,000 .ANG.) removes work-damaged material to the extent that after it is removed, and subsequent epitaxial layers are deposited over the exposed silicon, the stacking fault density in the epitaxial layer is low (less than 10 per sq.cm.).
U.S. Pat. No. 3,600,241 Doo et al deals with semiconductor device fabrication. After diffusion has been carried out at elevated temperatures through a SiO.sub.2 or another diffusion barrier mask, the mask is stripped from the surface of the semiconductor substrate and a surface of the semiconductor substrate is reoxidized. According to Doo et al, this eliminates surface defects in the semiconductor substrate which tend to arise at the elevated temperatures and over the relatively long periods of time necessary for diffusion. Where an epitaxial layer is to be formed on the surface of the substrate, the oxide layer is first removed from the surface. According to Doo et al this reduces stacking faults in the epitaxial layer caused by surface irregularities in the substrate.
U.S. Pat. No. 3,929,529 Poponiak discloses a method for gettering (removing) fast diffusing metal contaminants from a monocrystalline silicon body by a process which comprises anodizing at least one side of the body in an aqueous liquid bath under conditions that result in the formation of a porous silicon surface layer, annealing the resultant structure in a nonoxidizing environment for a time sufficient to trap the contaminants from within the semiconductor body into the porous silicon layer, and exposing the body to an oxidizing environment to oxidize the porous silicon layer to SiO.sub.2. The SiO.sub.2 layer can be removed, thereby completely removing the contaminants from the wafer or can be retained on the device since the contaminants are effectively tied up in the layer.
J. of Electrochemical Soc., Lifshitz, July 1983, pp. 1549-50, discloses a method for improving breakdown fields of oxides grown on reactive ion etched silicon surfaces. Lifshitz suggests growth of a thin oxide layer and its chemical removal prior to gate oxidation.
Other prior art of interest includes U.S. Pat. No. 4,023,266 Lovell and IBM Technical Disclosure Bulletin, Gettering of Impurities from Semiconductor Materials, Kastl et al, Vol. 12, No. 11, April 1970, p. 1983.